Problem: Simplify the following expression: $n = \dfrac{q}{2} - \dfrac{6q}{7}$
Solution: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $2$ and $7$ $\lcm(2, 7) = 14$ $ n = \dfrac{7}{7} \cdot \dfrac{q}{2} - \dfrac{2}{2} \cdot \dfrac{6q}{7} $ $n = \dfrac{7q}{14} - \dfrac{12q}{14}$ $n = \dfrac{7q -12q}{14}$ $n = \dfrac{-5q}{14}$